Current control systems of the machinery and processes of a facility in the papermaking industry generally run equipment and processes as fast as possible, while maintaining a set level of quality. The focus of control is on the current and historical operating characteristics of the particular piece of equipment, with a particular emphasis on output quality. The controls are sometimes designed to maintain maximum operating speed and the operator manually assesses and controls operations to maintain a targeted acceptable quality. Conversely, the controls may be designed to assess the operation of the equipment to assure that it is maintaining an acceptable quality of product while the operator forces the equipment to higher levels of production. In either case, the assumptions that faster is better (if quality is acceptable), underlies the prior art control systems. This is a faulty assumption: faster might actually be less desirable.
Controls are, therefore, designed to monitor, assess and aid in improvement of the quantitative and qualitative efficiency of the particular piece of equipment. For example, certain paper scanning devices are used on the finished end of a paper machine to determine if the paper product has adequate levels of dryness and basic uniformity. If these measurements detect a trend in the finished product towards unacceptable quality, the machine speed or other items may be automatically or manually adjusted (usually downward) to assure that adequate product quality is obtained. Similarly, the machine control system or operator personnel will monitor the amount of sheet breaks or excessive poor quality that occur on the machine. Again, speed or other items may be adjusted (usually downward) on the machine to reduce the number of breaks to assure that productive efficiency is achieved. Alternatively, if quality and the number of breaks are acceptable, the speed may be adjusted upward.
Production adjustments based on sheet breaks or subsequent roll quality problems discovered downstream are, however, predominately performed manually by operators who informally estimate whether the number of paper breaks or the quality deterioration is severe enough to merit adjustments, such as a reduction of machine speed. There are, in other words, no automated control systems that currently control the operating speed in response to productive efficiency of a paper machine.
An evaluation of the production efficiency is dependent on several variables and, therefore, an operator does not have all the necessary information to determine the ideal target operating speed. Thus, all adjustments based on efficiency are merely estimates to hopefully target ideal operating speed, even for the most experienced operators. Consequently, the operator unknowingly selects an operating speed based on a few obvious variables relating to inefficiencies. This selected speed may be, however, considerably far from the optimal operating speed. Further, changes to the operations that effect efficiency can occur rapidly, while manual reactions base on operator observations typically lag considerably behind. This lack of complete information and timely reaction greatly reduces the efficiency of the equipment operation.
While operating speed of a paper machine may be adjusted directly by control of the paper machine drive, it is often adjusted by changes to the steam pressure for the paper machine dryers. For example, when production is to be decreased, either manual input or machine controls first decrease the steam pressure in the dryer cans, which in turn increase the moisture content of the paper. As the moisture content increases, the machine's paper measuring system senses the moisture increase in the finished paper and automatically decreases the machine speed to allow for greater drying time. This, of course, has the same effect as decreasing the machine speed directly by slowing the paper machine drive motors. This is typical of many automatic adjustments to operating speed, which are affected by a forced change in quality, such as increased moisture content.
While unacceptable quality and sheet breaks occur at all acceptable paper machine operating speeds, increased frequency of breaks and diminishment of quality occurs as the operating speed increases. Current automated machine controls do not maximize efficiency by taking into account the loss of unacceptable quality and sheet breaks for determining the appropriate operating speed of a paper machine. Aside from providing information on sheet quality and sheet breaks, current machine and information system controls do not aid in the adjustment of the machine production to achieve the most efficient or optimal operating speed.
Similar situations occur through out a papermaking facility. Another example, for instance, is the control systems on a wood pulp digester. Pulp mill operators utilize current control equipment that measures, among other characteristics, the kappa number of pulp leaving the digester to determine an acceptable operating speed. As the production reaches or exceeds the digester's designed capacity, the kappa number increases. The pulp mill operators will set a limit on an acceptable higher-than-ideal limit on the Kappa number. This upper limit is established by understanding that additional delignification will occur in the subsequent bleaching process. While the higher limit may be established on a criteria that factors in an estimate of bleaching costs, the pulp mill control system does not actually calculate the cost of additional bleaching. There are no control features presently available that limit the digester operation speed based on the actual current marginal cost of the additional bleaching. Rather, pulp mill operators estimate the bleaching cost based on an average cost.
For example, it may be determined that the average additional bleaching activity required to achieve a certain level of additional delignification will cost $20 per ton of pulp, based on an average cost of bleaching. A pulp mill operator may, therefore, allow the digester to operate at a level that exceeds its capacity because such operation is considered efficient if the additional bleaching costs are actually $20 per ton. When all variables are considered, however, it may be discovered that the additional bleaching action required on a certain level of marginal operating speed may be measured to actually reach $100 per ton due to the non-proportional demands for bleaching chemicals, energy, and effluent treatment. Current controls do not calculate from the necessary variables the total additional bleaching cost on the marginal operating speed, and subsequently limit digester operations to not incur the additional inefficient bleaching.
Current equipment controls are utilized by paper manufacturing operators to control certain immediate inventories of items that are directly used by the equipment being controlled. For example, paper machine operating speed may be decreased manually or automatically by machine controls as high-density storage pulp inventory in front of the paper machine is decreased. When the machine controls recognizes an inventory depletion of pulp from high density storage, machine speed or steam pressure to the dryers may be limited to decrease machine operating speed to allow pulp storage to replenish or "catch-up" to desired levels of operation. This control of machine operating speed is, however, based solely on assuring adequate quantity of materials for continued operation, rather than any measure of operating speed based on efficiency.
One problem with current control systems is that they are strictly focused on either one particular piece of equipment's operating characteristics, or at best, focus on monitoring the availability of inflow materials for the piece of equipment. For example, the machine controls for a paper machine monitors the operating characteristics of the machine itself, primarily in the area of quality of the finished product. As discussed above, the controls may also monitor pulp inventory in high-density storage to help assure that inflows are available for continued operation. Current controls do not, however, monitor many, or even most, manufacturing inflows from the time of introduction into the process. For example, the availability of wood through recent purchases and all intervening steps throughout production from wood to pulp held in high density storage for the machine should be factored into the appropriate optimal operating speed of a paper machine. Similarly, a digester operating speed should be determined with a focus on the current efficiency of the bleach plant, based on its operating characteristics, to arrive at an efficient operating speed.
The current control systems also do not factor in many, or even most, events that occur with the product after it leaves the particular piece of equipment. For example, current controls of paper machines do not factor in the many activities that occur after the paper leaves the machine. Machine operating speeds are not, for example, tied to the finishing, inventorying and selling processes that occur after the paper leaves the paper machine. These activities should, however, have a significant effect on the operating speed of the machine, as the efficiency of the entire manufacturing process is relevant to any one component's operating speed.
To maximize operating efficiencies by optimizing the operating speed, control systems should link the entire manufacturing process activities together to analyze all, or as many as useful, potential variables. For a papermaking facility, these activities include the purchase of raw materials and the sales of finished goods. For example, the activity of procuring wood in the forest and the selling of finished product should be factored into the operating speed control of the paper machine and all other equipment.
An additional problem with current control systems is that any measured efficiency on marginal operating speed is based solely on quantitative and qualitative measurements, rather than total economic efficiency. While the quantitative and qualitative measurements are used to improve the economics of the concern, they do not include one other essential component of total economic efficiency, which is price.
In making equipment operating speed decisions, the current control systems fails to account for the price component of the economic efficiency of a particular activity. While productive and qualitative measurements of equipment operations are essential to establishing an appropriate efficient operating speed, the individual price components of input materials, processing or manufacturing, and value of outputs should also be factored into calculating the efficient operating speed of equipment. For example, under the current control system, additional steam showers may be added to the papermarking process on a paper machine to increase the operating speed. Current controls systems would dictate operating at the increased rate, without factoring the incremental use of the additional steam.
While the paper industry is the focus of the above examples, many additional industries have similar limitations in their current equipment control systems. These industries are similarly suffering from inefficiencies due to inadequate integrated control systems that factor in marginal operating speeds.